Resistance unit



Dec. 10, 1929; R. R. DUNLOP RESISTANCE UNIT Filed March 8 1924 Patented Dec. 10, 1929 UNITED I STATES I PATENT 'oFF-lcr.

ROBERT R. DUNLOP, or COLUMBUS, 01110, ASSIGNOR 'ro' JEFFREY MANUEACTUR- I ING COMPANY, 01 COLUMBUS, oHro, A CORPORATION or 01110 RESISTANCE UNIT Application filed March a,

The present invention relates to certain new and useful improvements in-resistance units, of the class which is especially adapted to use with electric motors, and similar apparatus, subject to the severe conditions obtaining in the narrowly limited space available in coal mines andthe like. I I

The especial object of this invention is to provide a wire resistance unit of large capacity and small dimensions, having great heat resisting capacity and mechanical strength combined with convenience and flexibility of design.

The means whereby I attain this object are fully set forth in the following specification and illustrated in the accompanying drawings of which- Fig. 1 is a side view of a resistance embodying my invention.

Fig. 2 is a view of the lateral edge of the device illustrated in Fig. 1, looking in the direction of the arrow of Figure 1. I

Fig. 3 is an end view of the device illustrated in Fig. 1. I

Fig. 1 is a sectional view taken along the line IVIV of Fig. 1.

Fig. 5 is a detail of the porcelain insulator forming a part of my improved resistance unit.

Fig. 6 is a fragmentary sectional view of a modified form of resistance unit coming within the spirit of my invention. 7

Like numerals refer to similar parts in the several figures.

In the drawings the numeral 1 refers to a frame, of generally rectangular outline, which is preferably made of cast iron but which may be formed of any other material suitable to the conditions of operation. Upon the frame 1 are mounted a plurality of porcelain insulating blocks 2 each having a longitudinal groove 3 adapted to engage the edges of the frame 1. The insulators 2 are preferably made in relatively short sections for convenience of manufacture, but if preferred they may be made in a single piece extending the length of the frame 1. The resistance wire 4 is wound upon the insulators 2 which are provided with spaced apart transverse grooves 5 adapted to receive the element resistance wire 4. with the conductors of an 1924. Serial No. 697,796.

relation to each other. Clamping members 6 and 7 drawn together by suitable means such as the machine screw 8, engage the insulator blocks 2 to hold them in position upon the frame 1. The clamping members 6 and 7 at the left hand end of Figure 1 are viewed from the back where the clamping screws 8 thereof do not show, the purpose of this arrangement being to bring the binding posts 9 of these two clamping members in position to receive the wire 1 more directly. Binding posts 9 formed'on the clamping members 6 afii'ord fastenings for the ends of the wire 4 whereby said wire is connected both electri-. cally and mechanically to said clamping members. Other binding posts 10 formed on the clamping members 6 serve to connect the external circuit. I e

The resistance wire 1 1s preferably composed of analloy having high specific resistance and low affinity for oxygen thereby adapting the resistance unit to use at temperatures producing a lowdegree of incandescence without'material deterioration. At

I such temperatures the buckling of the wire 4:

due to its expansion, may posslbly cause con- 1 tact between adjacent folds of said wire, causing shortcircuits and producing arcs which render the apparatus unfit for use in the explosive gaseous and dust laden atmosphere commonly encountered in coal mines, and tending to burn the wire and thereby destroy the-resistance unit. To prevent the forming of such. short circuits I have provided relatively short insulating collars, or beads 11 which are strung upon the wires 4 between i the insulators 2. These beads are formed of heat resisting insulating material, preferably of porcelain, and have an external diameter substantially equal to the space between alternate wires. These beads are spaced apart upon the wire 4 in such manner that the ends of the bead upon one fold of the wire engage the ends of the beads upon the adjacent folds thereby holdingthe beads in spaced relation to each other and exposing the greaterportion of the surface of the wire to the cooling effects of the atmosphere; The sleeves .11 on.

folds of said wire and hold them in spaced the end strands of resistance Wire are arranged in contact with each other, instead of being spaced as on the other strands, so as to retain the sleeves of adjacent strands in spaced relation to each other.

Formed on the frame 1, preferably at the corners: of. the frame, are laterally projecting bosses 12 having apertures through which the bolts 13 may project to attach the resistance unit to any preferred support such as the machine frame 14. Preferably there is interposed between the bolts 13 and the. metal of the frame 1 suitable insulators such as the mica tube 15 and the mica washerslfitofurther guard against electrical connection between the resistance wire 4 and the machine frame 1'4- If desired, two or more units may be stacked; together, as; shown in Fig. 1, the bolts 18 being of sufficient length to extend through the bosses 12 of all of the frames 1', and insulating Washers-117 may be inserted between adjacent; frames 1' to further guard against short. circuits.

Itistobe-unde'rstood that I donot limit nayself to the: precise construction above described, since these devices may be subject to wi'de variation without departure: from the spirit. of my invention. One such modification is shown in Fig. 6 ofthe drawing wherein divergent flangeslS are formed along the lateral edges of. the frame If, and the insul-ator blocks 2 are shaped to: fit the V-shaped grooves formed thereby.

By the above described construction I have provided a simple, durable and convenient resistanceunit, of small dimensions and great capacity, adapted to withstand the severe strains and shocks encountered in mining machine practice, and suitable for use in. the gaseous and dust laden atmosphere common- 1y found in coal mines and the like.

What I claim is 1' 1.. In: a resistance unit, the combination of a frame, insulating blocks arranged along outer substantially parallel edges of said frame, a resistance wire wound about said frame in contact with said blocks and tending to retain the latter against the edges of the frame, and interconnecting tension means other than the: resistance wire between opposite blocks for positively holding the latter against the frame edges.

21. In a resistance unit, the combination with a flat frame having two substantially parallel edges, insulating blocks positioned upon said parallel edges, a resistance wire wound around said frame-and engaging said blocks, and fastening means adapted to hold said insulating blocks in position upon said frame, said fastening means being also adapted to prevent the unwinding of'said: wire and to operatively connect it with the: conductors of an external circuit.

3. In a resistance unit, the combination with a fiat frame. having two substantially parallel edges, insulating blocks positioned upon said parallel edges, clamping members adapted to engage said insulating blocks and hold them in place upon said frame, a resistance wire wound around said frame and engaging said blocks, means to attach said wire to said clamping members, and separate means to connect said clamping member with the conductors of an external circuit.

4:. In a resistance unit, the combination of a frame, insulating bloc-ks arranged along outer substantially parallel edges of said frame, a resistance wire wound about said frame in contact. with said blocks and tending to retain the latter against the edges of the frame, and clamp means between opposite blocks for positively holding the latter against the frame edges, said clamp. means comprising; a' pair of substantially parallel arms and adjustable means for securing the intermediate portions of the arms together, the ends of the arms being engaged over the outer faces of'said blocks.

In testimony whereof I have hereunto set my hand.

ROBERT R. DUNLOP'. 

